The present invention relates in general to hybrid gas/electric vehicles, and, more specifically, to controlling the transition from electric-only mode to modes using the gas combustion engine in a manner that avoids premature or excessive switching to a gas engine mode.
A driver-controlled “accelerator” pedal is a common input device in all types of transportation vehicles such as gas-powered cars and trucks, electric vehicles, and hybrids. The pedal is typically operated by the driver's foot but may also be controlled by hand, for example. Historically, a pedal position corresponded directly to a position of a throttle supplying fuel and air to a combustion engine. In modern vehicles having electronic controls and additional types of powertrains, the relationship between the amount of pedal depression and the powertrain response can be tuned to provide different speed and torque responses.
An approach for adjusting a pedal position map is disclosed in U.S. Pat. No. 6,654,677 to Weber et al. A powertrain controller varies the mapping of an accelerator pedal position to an electronic throttle angle based on vehicle speed in order to improve operator control over vehicle speed, torque output, and acceleration. At lower vehicle speeds, the pedal position is mapped to the electronic throttle angle with a focus on providing acceleration control. At higher vehicle speeds, the pedal position is mapped to the electronic throttle angle with a focus on controlling vehicle speed.
The map between pedal position and wheel or engine output can be dynamically adjusted in response to additional variables. In U.S. application publication 2013/0197775A1, the relationship is adjusted based on road grade.
More generally, the mapping relationship varies the sensitivity of pedal position changes to corresponding changes in wheel/engine output. For example, the driver's perception of a vehicle's capability and responsiveness may be positively impacted by a pedal mapping with a steep slope, resulting in large changes in wheel power demands at relatively small accelerator pedal position changes. A pedal mapping with a small slope can provide a higher level of controllability, requiring larger changes in accelerator pedal position to realize a significant change to the driver demanded wheel power.
With the ever increasing need to produce vehicles that are more fuel efficient, hybrid electric vehicles (HEV's) have become popular because they provide an improvement in fuel economy over many conventional vehicles that utilize only an internal combustion engine to drive the vehicle. One of the primary advantages of an HEV is that it allows the vehicle to be powered by an electric motor under certain operating conditions. For example, when the wheel output demand is relatively moderate and the battery or other electrical power source is sufficiently charged, the engine may be shut off and the vehicle driven exclusively by one or more electric motors. As operating conditions change, the engine may be started to provide additional power.
With the HEV being driven in an electric-only mode, a control system determines when to start and stop the engine based on many inputs. For example, in a power-split or parallel hybrid one of the primary inputs is the driver demanded wheel power (based on a mapping of pedal position). When the wheel power demand exceeds a threshold known as the engine pull-up threshold, the engine is started to provide propulsion for the vehicle. Other inputs which may also be used to start the engine include the state of charge (SOC) of the high voltage battery, climate control demands for power or heat, or detected engine conditions in which continued operation is needed to maintain reduced emissions.
If an accelerator pedal mapping is too sensitive to small changes in accelerator pedal position, then small or inadvertent changes in accelerator pedal position may trigger an engine start while driving at a driver demand power that is near the engine pull-up threshold. In most circumstances it is beneficial to maximize the time spent in electric mode for improved efficiency and to improve owner satisfaction with the vehicle. Thus, it is desirable to provide controllability (less sensitivity) near the pull-up threshold, as has been suggested in U.S. patent publication 2013/0024061. In this publication, a mapping for suppressing engine activation can be selected using an ECO switch. However, the selected mapping is fixed and only functions with a fixed threshold for activating the engine.
It is advantageous to employ a dynamic pull-up threshold which can change based on many different conditions, including some which do not influence the accelerator pedal map such as the battery state of charge. The prior art has failed to accomplish both an optimum responsiveness and engine start controllability because of the static pull-up threshold and accelerator pedal mapping.